SB

iTrader: (1)

I'm a believer that total timing on a NA engine should be at (or max 2 degrees less) where the motor wants it. Fuel octane should be changed to one that the motor does not detonate on.

Many stock BBC rect port heads on performance applications like 38-40 total timing. If ported with better chamber work this # may reduce.

Many aftmkt heads have much more effecient chambers and will run best with 35-36 degrees timing.

One engine is not another engine - there is more too timing requirements than just parts bolted on.

scarrab30

nordicflame, I dont think its your cam you probably need a good carb tuner. My motors idle@1000, in gear600. I run alot more cam than most.269-276 @50 .693-709 lift on110+2. Ialso run msd ignition with the advance free weighted. A single 1050 carb with alot of bleed work.

Nordicflame

iTrader: (4)

Thanks for the reply guys.
I will richen it up and switch the curve for him and see how she does.
The carb was just rebuilt and tuned by Mesa. I think the idle would be hard to hit off of a bench because we are at 5000 feet elevation
Thanks,
Dave

SB

iTrader: (1)

Nordicflame - don't forget to use the secondaries idle speed screw to your advantage . Many idle issues can be cleared up with adding some more air thru them during idle. You'll then be able to lower primaries a touch and have more sensitivity on the idle mixture screws while still getting enough air past throttle blades.

If you don't lock out your timing, I'm going to guess you'll need somewhere around 18-20° at idle.

brek0054

Hi i have some problems!!what is wrong my total is only 23 degress!i have thunderbolt 4,can i have done somthing wrong wiring?

nocigarette

Dont Y Want To Know Timing On A Blower Motor, Ratman???????????????????????????????????????????? ??????????????



Mine 540 Na
34deg
Always Premium
702hp Really 660-680
Dart Heads
Jesel Rollers Stud Guides

nordic95

Hey guys,


I dont mean to hijack this thread but I have the same question about timing.My motors on dyno pulled most HP at 28 degrees total.So this is where Im running them right now.I really think I should be around 34 to 36 according to what you guys are posting.I have MSD distrib. set with 9 degrees advance,so Im at 19 initial and 28 total.Boat runs well but it dont seem to have the rpms Im looking for.I wonder if this is what is causing it.How can I tell for sure if I am detonating or not when I move the timing?

502 mag
Edelbrock aluminum heads
9.8 ratio
631 hp on dyno w/o accesories and dry exhaust,about 575hp in boat
crane 651 cam
revolution marine exhaust

Thanks in advance

jdnca1

Nordic

NA 502's seem to like 34-36 degrees....turn it up to 34 and see if you can pull more rpm....you will not come close to hurting anything there. Mercury puts 36 degrees in their iron headed 500EFI's directly from the factory and they tell you to run 87....and speaking from experience they run better on 87.

nordic95

What is the comp. ratio on the 500?I think mine should be a little more tolerable with alumin. heads?

SB

iTrader: (1)

Combustion chamber design, spark plug placement, piston design, and machine work has a ton to do with timing. OE motors are mass produced so basing two exact motors to each other (same crate motor) is typically fine.

Basing one builder built aftmkt engine to another is not valid.

Timing is not just about detonation. It's about drivability, effeciency, and overall power.

Say, your 11:1 BBC engine produces best overall power / effeciency at 38 degrees total timing, however you run into detonation. Is it better to take a bunch of timing out or run required fuel octane ? If you can't get the required octane fuel, then the engine was not built correctly for your needs.